Done the quiet line test, there is an extremely quiet "fuzz" in the background. Whether this constitues as noise, or whether its as a result of the crap £20 handset I bought, couldn't tell you, but it is all wired and only powered by the line. (connected to test socket)
As well as that when the menu options were going and this is only once, I heard a loud squeal, sort of like when a capacitor is ready to blow which is sort of strange.
SoGEA line is dead, as expected, figured it didn't hurt to try though
Anyway spoke to Sky and explained everything and to my shock (I really thought they'd be telling me to get on to IDNet to get this sorted!) they agreed to send out an OR engineer and explicitly said there would be no charge.
I was actually going to leave Sky mainly for their craptastic support but it's starting to feel like a grass is greener situation now.
Edit - Just to see, tried it with the filter on, it made a ton of different sounds, whether that's expected with the filter actually on, I'm not sure.
Also not sure if it would effect the second line too? Maybe it is as simple as bad filter and that's triggered some hardcore DLM?